Three Shaft Connection Types for Helical Gears
A helisel dişli is connected to its shaft by one of three mechanisms, each suited to a different torque range and assembly frequency:
A rectangular steel key sits in matched keyways in both the shaft and the helisel dişli bore, transmitting torque through the key’s shear area. Bore tolerance H7 (clearance fit) — the gear can be slid on and off the shaft by hand or light press. Suitable for gears requiring periodic removal for maintenance. This is the default connection for industrial helisel dişliler in M3–M32.
Bore tolerance P7 or R7 — the helisel dişli is pressed or shrink-fitted onto the shaft with 0.01–0.05 mm of radial interference. Torque is transmitted by friction at the shaft-bore interface; no key is used. Advantages: no stress concentration from keyway; full bore area available for torque; no fretting at key contact. Disadvantages: requires hydraulic press or heating for installation and removal. Used for permanent high-torque connections in heavy industry.
An involute spline (DIN 5480) with many small teeth around the bore perimeter distributes the torque over a large contact area, allowing much higher torque than a single key at the same shaft diameter, while remaining easily disassembled. Used for high-torque vehicle driveshaft connections, crane gearboxes, and any application where the helisel dişli must be removed and reinstalled repeatedly without special equipment.
DIN 6885-1 Parallel Key Dimensions — Reference Table
DIN 6885 Part 1 specifies the standard parallel key (Passfeder) dimensions for a given shaft diameter. The key width b and height h are selected from the standard table based on the shaft diameter at the helisel dişli bore:
| Shaft Diameter Range (mm) | Key Width b (mm) | Key Height h (mm) | Depth in Shaft t₁ (mm) | Depth in Hub t₂ (mm) |
|---|---|---|---|---|
| 17–22 | 6 | 6 | 3.5 | 2.8 |
| 22–30 | 8 | 7 | 4.0 | 3.3 |
| 30–38 | 10 | 8 | 5.0 | 3.3 |
| 38–44 | 12 | 8 | 5.0 | 3.3 |
| 44–50 | 14 | 9 | 5.5 | 3.8 |
| 50–58 | 16 | 10 | 6.0 | 4.3 |
| 58–65 | 18 | 11 | 7.0 | 4.4 |
| 65–75 | 20 | 12 | 7.5 | 4.9 |
| 75–85 | 22 | 14 | 9.0 | 5.4 |
| 85–95 | 25 | 14 | 9.0 | 5.4 |
| 95–110 | 28 | 16 | 10.0 | 6.4 |
| 110–130 | 32 | 18 | 11.0 | 7.4 |
| 130–150 | 36 | 20 | 12.0 | 8.4 |
| 150–170 | 40 | 22 | 13.0 | 9.4 |
Source: DIN 6885-1:2019 (Form A, flat top key, rounded ends). t₁ = keyway depth in shaft, t₂ = keyway depth in hub (helisel dişli bore). The key height h projects into both shaft and hub keyways; the total engagement depth = t₁ + t₂ ≈ h with a small clearance at the key top.
Bore Tolerance Selection — H7, K7 and P7 Explained
Helical gear shaft connection — the bore tolerance (H7 clearance, K7 transition, or P7 interference) determines the assembly method and torque capacity at the bore-shaft interface. The DIN 6885-1 key transmits torque in H7 clearance fit assemblies; interference fit connections transmit torque by friction without any key
| Bore Tolerance (ISO 286-1) | Fit Type | Clearance or Interference at ⌀50 mm | Assembly Method | Ne zaman belirtmelisiniz? |
|---|---|---|---|---|
| H7 | Clearance (with h6 shaft) | +0.000 / +0.025 mm clearance | Hand push or light mallet; key transmits torque | Standard removable helisel dişli; key required for torque |
| K7 | Transition (with k6 shaft) | −0.002 / +0.023 mm (transition) | Light press; key reinforces torque capacity | Reduced vibration/fretting risk vs H7; moderate disassembly frequency |
| M7 | Transition / light interference | −0.009 / +0.016 mm | Press (hydraulic preferred) | Infrequent removal; better torque retention than H7+key for reversing loads |
| P7 | Interference | −0.026 / −0.001 mm interference | Hydraulic press (10–30 tonnes); or heat the gear 150–200°C | Permanent or rare-removal connection; heavy-duty reversing loads; no key needed at moderate torque |
| H6 | Precision clearance | +0.000 / +0.016 mm (tighter than H7) | Selective fit — must pair with matched shaft | Precision indexing or register; servo gearboxes where concentricity is critical |
Minimum Wall Thickness — Bore to Root Circle
The wall thickness between the helisel dişli bore and the gear root circle must be sufficient to prevent cracking at the tooth root during heat treatment (thermal gradients through thin sections cause residual stresses that can lead to quench cracking) and to prevent hub face yielding under the contact pressure of the press-fit connection:
Minimum wall thickness: t_wall ≥ 2.5 × Mn (Korea Ever-Power standard for carburized gears)
t_wall ≥ 2.0 × Mn (minimum for QT gears under moderate load)
Checking the wall:
Root circle diameter d_f = Mn × (z − 2.5) / cos β (standard dedendum 1.25 × Mn)
Maximum bore diameter d_bore_max = d_f − 2 × t_wall_min
Example: M8, z=30, β=20°, carburized:
d_f = 8 × (30 − 2.5) / cos20° = 8 × 27.5 / 0.9397 = 234.1 mm
t_wall_min = 2.5 × 8 = 20 mm
d_bore_max = 234.1 − 2 × 20 = 194.1 mm
A bore larger than 194 mm on this example helisel dişli would violate the minimum wall thickness and risk quench cracking during carburizing, or hub face yielding under press-fit installation. Korea Ever-Power checks the wall thickness constraint at the drawing review stage and flags any bore-module combination that violates the minimum before production begins.
Double Keyway — For Very High Torque on Large Module Gears
When the torque requirement exceeds the capacity of a single DIN 6885-1 key at the given shaft diameter, two keys placed diametrically opposite (180° apart) double the total key contact area and halve the shear stress per key. Double keyways are standard for helisel dişliler with shaft diameters above approximately 150 mm in high-torque drives. The two keyways must be positioned at exactly 180° — measured and verified by CMM after machining. An angular error between the two keyways greater than ±0.1° creates unequal key loading that effectively reduces the double-key torque capacity to approximately 1.6× rather than 2× the single-key value.
DIN 5480 Spline Connection — When to Choose Spline Over Key
A DIN 5480 involute spline hub replaces the single keyway with 10–80 small involute-profile spline teeth around the bore perimeter. The torque capacity of a spline exceeds a single key by 3–8× at the same shaft diameter, because the torque is distributed over many teeth rather than concentrated on one key. Select spline over key when:
- Frequent disassembly is required: Spline connection can be assembled and disassembled without special tools (slide fit spline) while still transmitting very high torque — combining the torque capacity of an interference fit with the removability of an H7 clearance fit. Common in vehicle driveshaft and crane gearbox applications.
- Very high torque at moderate shaft diameter: Bir helisel dişli with shaft diameter 100 mm transmitting 5,000 N·m, a single DIN 6885-1 key (28 × 16 mm) would be sheared at the key root fillet. A DIN 5480 spline with 20 teeth of module 2.5 provides 10–15× more torque capacity at the same 100 mm shaft diameter.
- Precision angular positioning: DIN 5480 diameter-centered splines (centering on the spline OD) provide concentricity within 0.005–0.015 mm between the gear and shaft — better than an H7 key connection which allows slight bore-to-shaft concentricity variation from the clearance.
Korea Ever-Power — Bore and Keyway Machining as Standard
Korea Ever-Power CNC machining of helisel dişli bore and DIN 6885-1 keyway — the bore is finish-bored to H7 tolerance (verified by calibrated bore gauge), the keyway is broached to the exact b × h dimensions from the DIN 6885-1 table for the shaft diameter, and the wall thickness is confirmed against the 2.5 × Mn minimum before final delivery
Korea Ever-Power machines the bore, keyway, and hub dimensions of every helisel kesme dişlisi order to the customer’s drawing specification. Standard processing: bore to H7 tolerance (confirmed by bore gauge and CMM), DIN 6885-1 keyway broached to h9 tolerance, keyway position verified at 90° and 180° reference as requested, wall thickness confirmed against 2.5 × Mn minimum. Korea Ever-Power also machines DIN 5480 spline bores and interference-fit (P7) bores for heavy-duty applications. As a direct helisel dişli üreticisi, bore machining is performed after tooth grinding as the final machining operation — ensuring that bore concentricity and keyway angular position are measured relative to the finished gear tooth reference, not the pre-grind blank. Browse the helisel dişli ürün yelpazesi for all bore and connection configurations.
Sıkça Sorulan Sorular
For dynamic balance, the keyway position relative to the tooth does matter on high-speed helisel dişliler. The keyway removes a small asymmetric mass from the bore — approximately 0.5–2% of the gear body mass depending on module and hub wall thickness. On helisel dişliler running above 1,500 RPM, this asymmetric mass can cause a measurable imbalance that excites 1× shaft frequency vibration. Korea Ever-Power offers dynamic balancing of completed helisel dişliler to ISO 21940 balance grade G6.3 or better for all gears with pitch-line velocity above 10 m/s, typically by removing a small amount of material from the opposite side of the hub face. The keyway angular position is documented in the order file so that the balance correction location is recorded and reproducible for future replacement gears.
For a 60 mm shaft: DIN 6885-1 key = 18 × 11 mm (from the 58–65 mm shaft diameter range). The key shear area = b × L_key × τ_allowable, where L_key is the effective key engagement length (equal to the helisel dişli face width b, but not exceeding the recommended key length from DIN 6885-1 for the shaft diameter). For a steel key in a steel shaft and hub, τ_allowable ≈ 60–100 N/mm² (depending on load type — static or cyclic). For b = 18 mm, L_key = 50 mm (face width), τ = 80 N/mm²: Key shear force = 18 × 50 × 80 = 72,000 N; Torque capacity T = Force × shaft_radius = 72,000 × 0.030 = 2,160 N·m. For higher torques on 60 mm shaft, use K7 or M7 fit (adds bore-shaft friction), or use DIN 5480 spline connection.
For a P7 bore on a 50 mm shaft (k6 shaft tolerance), the nominal interference is 0.017 to 0.042 mm radially. The friction torque capacity of this interference fit: T_friction = f × π × d_bore × L_hub × p × (d_bore / 2), where p = interference pressure = E × δ × (d_bore)^(−1) × wall factor [MPa], f = friction coefficient ≈ 0.12–0.15 (oil-free steel-steel, press assembly). For 50 mm bore × 0.03 mm interference × 40 mm hub length: p ≈ 210 GPa × 0.03 / (50 × wall correction) ≈ 50–70 MPa; T ≈ 0.13 × π × 50 × 40 × 60 × 25 ≈ 1,220 N·m. This is approximately 60% of the equivalent key connection torque — but the interference fit transmits torque without any stress concentration at the keyway, giving better fatigue performance under reversing or cyclic torque. Korea Ever-Power provides the theoretical torque capacity calculation for any P7 interference fit helisel dişli bore on request.
Yes — provided the new larger bore does not violate the minimum wall thickness (2.5 × Mn from bore to root circle). The bore is re-bored on a CNC turning centre after all heat treatment and grinding is complete, then the keyway is re-broached to the DIN 6885-1 dimensions for the new shaft diameter. If the bore enlargement requires widening the keyway: both the keyway width and depth change per DIN 6885-1 for the new shaft diameter range. Korea Ever-Power offers bore enlargement as a modification service on any previously supplied helisel dişli, subject to the wall thickness check. Cost is typically 20–35% of a new gear order — significantly less expensive than ordering a new gear when only the bore size has changed.
Bore, Keyway and Hub Specification for Your Helical Gear
Provide your shaft diameter, transmitted torque, assembly frequency, and connection type preference. Korea Ever-Power confirms the correct DIN 6885-1 key dimensions, bore tolerance class, and wall thickness check before production begins — as standard at the drawing review stage.
H7/K7/P7 bore · DIN 6885-1 key · DIN 5480 spline · Double keyway · Wall thickness check · Balance grade G6.3 available
Editör: Cxm
